In 2018, Susan's sole proprietorship earns $300,000 of self-employment net income (after the deduction for one-half of self-employment tax).

a. The maximum amount that Susan can deduct for contributions to a defined contribution Keogh plan is?

b. Suppose Susan contributes more than the allowable amount to the Keogh plan. What are the consequences to her?

Contributions in excess of the allowable amount under 415 are not deductible, and they may be subject to a _______ % excise tax.